Arrival of rabbit haemorrhagic disease virus 2 to northern Europe: Emergence and outbreaks in wild and domestic rabbits (Oryctolagus cuniculus) in Sweden

First report of GI.1aP-GI.2 recombinants of rabbit hemorrhagic disease virus in domestic rabbits in China

The rabbit hemorrhagic disease virus 2 (RHDV2 or GI.2) is a highly contagious agent leading to lethal disease in rabbits. It frequently recombines with other Lagovirus genus, generating epidemical variants with high pathogenicity. In this study, twenty-two liver samples tested positive for GI.2 VP60 gene, were collected in rabbit farms from several geographical regions in China. All GI.2 positive specimens were submitted for RT-PCR detection, nucleotide sequencing and phylogenetic analysis. In addition, suspected GI.2 recombinants were evaluated for virus virulence. The results showed that nine presumptive recombinants were identified by testing for RdRp-VP60 recombination. In these recombinants, four were selected to fully characterize the genome of novel GI.2 recombinant variants, which were described as GI.1aP-GI.2. The nucleotide sequence of these novel variants showed unique recombination pattern and phylogenetic features compared to currently prevalent GI.2 variants. Furthermore, this distinctive recombination of new variant SCNJ-2021 moderately enhanced the virulence of GI.2, even for rabbits vaccinated against parental GI.2. In conclusion, the novel GI.1aP-GI.2 recombinants were identified in rabbit industry in China for the first time, which expanded the knowledge on the phylodynamics and genomic diversity of GI.2 genotype. The rapid molecular evolution and varied pathogenicity of these virus recombinants highlight the urgent need for epidemiological surveillance and for future prevention of these neglected GI.2 variants.

Confirmation of the Rabbit Hemorrhagic Disease Virus Type 2 (GI.2) Circulation in North Africa

Rabbit hemorrhagic disease (RHD) is a highly contagious viral disease that causes fatal acute hepatitis in domestic and wild lagomorphs. It has taken on major economic importance in countries like Morocco. In addition to the classical virus (RHDV), a novel emerged genotype (RHDV2) is circulating, especially in the north shore of the Mediterranean basin since 2010. Many small animal farmers reported clinical cases from several rabbitries in Agadir (Morocco) despite systematic vaccination against the RHDV. The main objective was to characterize the current RHDV strains circulating in the studied area to help to choose an adequate vaccine. For that, we extracted viral RNA from rabbit livers, carried out the PCR analyses, and we sequenced the viral structural capsid protein (VP60) of the RHDV. The phylogenetic analysis results allowed us to state that the novel genotype (RHDV2) is circulating in the studied geographical area, and to characterize the isolated sequences. As a conclusion, we recommend updating RHD epidemiological relating data and reviewing the vaccine protocols by both targeting RHDV (GI.1) and RHDV2 (GI.2) in any future preventive program.

Potent Protease Inhibitors of Highly Pathogenic Lagoviruses: Rabbit Hemorrhagic Disease Virus and European Brown Hare Syndrome Virus

Rabbit hemorrhagic disease (RHD) and European brown hare syndrome (EBHS) are highly contagious diseases caused by lagoviruses in the Caliciviridae family. These infectious diseases are associated with high mortality and a serious threat to domesticated and wild rabbits and hares, including endangered species such as riparian brush rabbits (Sylvilagus bachmani riparius). In the United States (U.S.), only isolated cases of RHD had been reported until Spring 2020. However, RHD caused by GI.2/rabbit hemorrhagic disease virus (RHDV)2/b was unexpectedly reported in April 2020 in New Mexico and has subsequently spread to several U.S. states, infecting wild rabbits and hares and making it highly likely that RHD will become endemic in the U.S. Vaccines are available for RHD; however, there is no specific treatment for this disease. Lagoviruses encode a 3C-like protease (3CLpro), which is essential for virus replication and a promising target for antiviral drug development. We have previously generated focused small-molecule libraries of 3CLpro inhibitors and demonstrated the in vitro potency and in vivo efficacy of some protease inhibitors against viruses encoding 3CLpro, including caliciviruses and coronaviruses. Here, we report the development of the enzyme and cell-based assays for the 3CLpro of GI.1c/RHDV, recombinant GI.3P-GI.2 (RHDV2/b), and GII.1/European brown hare syndrome virus (EBHSV) as well as the identification of potent lagovirus 3CLpro inhibitors, including GC376, a protease inhibitor being developed for feline infectious peritonitis. In addition, structure-activity relationship study and homology modeling of the 3CLpro and inhibitors revealed that lagovirus 3CLpro share similar structural requirements for inhibition with other calicivirus 3CLpro. IMPORTANCE Rabbit hemorrhagic disease (RHD) and European brown hare syndrome (EBHS) are viral diseases that affect lagomorphs with significant economic and ecological impacts. RHD vaccines are available, but specific antiviral treatment for these viral infections would be a valuable addition to the current control measures. Lagoviruses encode 3C-like protease (3CLpro), which is essential for virus replication and an attractive target for antiviral drug discovery. We have screened and identified potent small-molecule inhibitors that block lagovirus 3CLpro in the enzyme- and cell-based assays. Our results suggest that these compounds have the potential for further development as antiviral drugs for lagoviruses.

The outbreak of rabbit hemorrhagic virus type 2 in the interior of China may be related to imported semen

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We identified one RHD case caused by a new RHDV variant (GI.2) in China through HA, TEM, and genome sequencing.

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This is the first study to demonstrate that GI.2 can replicate efficiently in the reproductive system.

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Our evidence suggests that GI.2 might be introduced into China by contaminated rabbit semen.

Comparative susceptibility of eastern cottontails and New Zealand white rabbits to classical rabbit haemorrhagic disease virus (RHDV) and RHDV2

Rabbit haemorrhagic disease virus (RHDV) is associated with high morbidity and mortality in the European rabbit (Oryctolagus cuniculus). In 2010, a genetically distinct RHDV named RHDV2 emerged in Europe and spread to many other regions, including North America in 2016. Prior to this study it was unknown if eastern cottontails (ECT(s); Sylvilagus floridanus), one of the most common wild lagomorphs in the United States, were susceptible to RHDV2. In this study, 10 wild-caught ECTs and 10 New Zealand white rabbits (NZWR(s); O. cuniculus) were each inoculated orally with either RHDV (RHDVa/GI.1a; n = 5 per species) or RHDV2 (a recombinant GI.1bP-GI.2; n = 5 per species) and monitored for the development of disease. Three of the five ECTs that were infected with RHDV2 developed disease consistent with RHD and died at 4 and 6 days post-inoculation (DPI). The RHDV major capsid protein/antigen (VP60) was detected in the livers of three ECTs infected with RHDV2, but none was detected in the ECTs infected with RHDV. Additionally, RHD viral RNA was detected in the liver, spleen, intestine and blood of ECTs infected with RHDV2, but not in the ECTs infected with RHDV. RHD viral RNA was detected in urine, oral swabs and rectal swabs in at least two of five ECTs infected with RHDV2. One ECT inoculated with RHDV2 seroconverted and developed a high antibody titre by the end of the experimental period (21 DPI). ECTs inoculated with the classic RHDV did not seroconvert. In comparison, NZWRs inoculated with RHDV2 exhibited high mortality (five of five) at 2 DPI and four of five NZWRs inoculated with RHDV either died or were euthanized at 2 DPI indicating both of these viruses were highly pathogenic to this species. This experiment indicates that ECTs are susceptible to RHDV2 and can shed viral RNA, thereby suggesting this species could be involved in the epidemiology of this virus.

Clinical and pathologic findings in an outbreak in rabbits of natural infection by rabbit hemorrhagic disease virus 2 in the northwestern United States

Rabbit hemorrhagic disease virus 2 (RHDV2) causes an often-fatal disease of rabbits that has resulted in outbreaks in rabbitries in Europe, Africa, Australia, and Asia. RHD has historically been characterized as a foreign animal disease in the United States. In July 2019, RHDV2 was detected in rabbits on Orcas Island along the northwestern coast of Washington (WA) State following reports of deaths in multiple feral and domestic rabbits. We document and highlight here the unique clinical presentation and gross and histologic lesions observed in this recent WA outbreak. Affected rabbits died without premonitory signs or displayed hyporexia and/or lethargy for ≤1 d prior to death. The most consistent pathologic finding was random, multifocal hepatocellular necrosis, often with concurrent multifocal-to-diffuse splenic necrosis. The lack of significant clinical signs in conjunction with the random distribution of hepatic necrosis in the WA outbreak contrasts with previous reports of RHDV2 disease progression.

Incursions of rabbit haemorrhagic disease virus 2 in Canada-Clinical, molecular and epidemiological investigation

Rabbit haemorrhagic disease virus 2 (RHDV2) is a newly emerging Lagovirus belonging to the family Caliciviridae. After its first discovery in 2010 in France, this highly pathogenic virus rapidly spread to neighbouring countries and has become the dominant strain, replacing the classical RHDV strains. RHDV2 was first reported in North America in 2016 in Mont-Joli, Quebec, Canada, and it was reported again in 2018 and 2019 on Vancouver Island and the southwest mainland of British Columbia (BC). The whole genome sequence of the RHDV2 Quebec isolate resembled the 2011 RHDV2-N11 isolate from Navarra, Spain with 97% identity at the nucleotide level. The epidemiological investigation related to this outbreak involved three hobby farms and one personal residence in Quebec. In February 2018, high mortality was reported in a large colony of feral rabbits on the Vancouver Island University Campus, Nanaimo, BC. The virus identified showed only 93% identity to the Quebec RHDV2 isolate at the nucleotide level. Additional cases of RHDV2 on Vancouver Island and on the BC mainland affecting feral and captive domestic, and commercial rabbits were reported subsequently. Vaccination was recommended to control the outbreak and an inactivated bivalent vaccine was made available to the private veterinary practices. In June 2019, an isolated RHDV2 outbreak was reported in pet rabbits in an apartment building in Vancouver, BC. This virus showed only 97% identity to the RHDV2 isolates responsible for the BC outbreak in 2018 at the nucleotide level, suggesting that it was an independent incursion. The outbreak in BC killed a large number of feral European rabbits; however, there were no confirmed cases of RHD in native rabbit species in BC.

Changes in virus transmission dynamics following the emergence of RHDV2 shed light on its competitive advantage over previously circulating variants

Rabbit haemorrhagic disease virus (RHDV) is highly pathogenic to European rabbits. Until recently, only one serotype of RHDV was known, GI.1/RHDV. RHDV2/GI.2 is a novel virus that has rapidly spread and become the dominant pathogenic calicivirus in wild rabbits worldwide. It is speculated that RHDV2 has three competitive advantages over RHDV: (a) the ability to partially overcome immunity to other variants; (b) the ability to clinically infect young rabbits; and (c) a wider host range. These differences would be expected to influence virus transmission dynamics. We used markers of recent infection (IgM/IgA antibodies) to investigate virus transmission dynamics pre and post the arrival of RHDV2. Our data set contained over 3,900 rabbits sampled across a 7-year period at 12 Australian sites. Following the arrival of RHDV2, seasonal peaks in IgM and IgA seropositivity shifted forward one season, from winter to autumn and spring to winter, respectively. Contrary to predictions, we found only weak effects of rabbit age, seropositivity to non-pathogenic calicivirus RCV-A1 and population abundance on IgM/IgA seropositivity. Our results demonstrate that RHDV2 enters rabbit populations shortly after the commencement of annual breeding cycles. Upon entering, the population RHDV2 undergoes extensive replication in young rabbits, causing clinical disease, high virus shedding, mortality and the creation of virus-laden carcasses. This results in high virus contamination in the environment, furthering the transmission of RHDV2 and initiating outbreaks, whilst simultaneously removing the susceptible cohort required for the effective transmission of RHDV. Although RHDV may enter the population at the same time point, it is sub-clinical in young rabbits, causing minimal virus shedding and low environmental contamination. Our results demonstrate a major shift in epidemiological patterns in virus transmission, providing the first evidence that RHDV2's ability to clinically infect young rabbits is a key competitive advantage in the field.

Immunity against Lagovirus europaeus and the Impact of the Immunological Studies on Vaccination

In the early 1980s, a highly contagious viral hemorrhagic fever in rabbits (Oryctolagus cuniculus) emerged, causing a very high rate of mortality in these animals. Since the initial occurrence of the rabbit hemorrhagic disease virus (RHDV), several hundred million rabbits have died after infection. The emergence of genetically-different virus variants (RHDV GI.1 and GI.2) indicated the very high variability of RHDV. Moreover, with these variants, the host range broadened to hare species (Lepus). The circulation of RHDV genotypes displays different virulences and a limited induction of cross-protective immunity. Interestingly, juvenile rabbits (<9 weeks of age) with an immature immune system display a general resistance to RHDV GI.1, and a limited resistance to RHDV GI.2 strains, whereas less than 3% of adult rabbits survive an infection by either RHDV GI.1. or GI.2. Several not-yet fully understood phenomena characterize the RHD. A very low infection dose followed by an extremely rapid viral replication could be simplified to the induction of a disseminated intravascular coagulopathy (DIC), a severe loss of lymphocytes—especially T-cells—and death within 36 to 72 h post infection. On the other hand, in animals surviving the infection or after vaccination, very high titers of RHDV-neutralizing antibodies were induced. Several studies have been conducted in order to deepen the knowledge about the virus’ genetics, epidemiology, RHDV-induced pathology, and the anti-RHDV immune responses of rabbits in order to understand the phenomenon of the juvenile resistance to this virus. Moreover, several approaches have been used to produce efficient vaccines in order to prevent an infection with RHDV. In this review, we discuss the current knowledge about anti-RHDV resistance and immunity, RHDV vaccination, and the further need to establish rationally-based RHDV vaccines.

Retrospective Analysis Shows That Most RHDV GI.1 Strains Circulating Since the Late 1990s in France and Sweden Were Recombinant GI.3P-GI.1d Strains

Recombination is one of the major sources of genetic variation in viruses. RNA viruses, such as rabbit hemorrhagic disease virus (RHDV), are among the viruses with the highest recombination rates. Several recombination events have been described for RHDV, mostly as a consequence of their genomic architecture. Here, we undertook phylogenetic and recombination analyses of French and Swedish RHDV strains from 1994 to 2016 and uncovered a new intergenotypic recombination event. This event occurred in the late 1990s/early 2000s and involved nonpathogenic GI.3 strains as donors for the nonstructural part of the genome of these recombinants, while pathogenic GI.1d strains contributed to the structural part. These GI.3P-GI.1d recombinant strains did not entirely replace GI.1d (nonrecombinant) strains, but became the dominant strains in France and Sweden, likely due to a fitness advantage associated with this genomic architecture. GI.3P-GI.1d (P stands for polymerase) strains persisted until 2013 and 2016 in Sweden and France, respectively, and cocirculated with the new genotype GI.2 in France. Since strains from the first GI.2 outbreaks were GI.3P-GI.2, we hypothesize that GI.3P-GI.1d could be the parental strain. Our results confirm the outstanding recombination ability of RHDV and its importance in the evolution of lagoviruses, which was only revealed by studying complete genomic sequences.

Emergence of rabbit haemorrhagic disease virus 2 in China in 2020

Rabbit haemorrhagic disease (RHD) is an acute fatal disease caused by the Lagovirus rabbit haemorrhagic disease virus (RHDV), which was first reported in 1984 in China. Strains of two different genotypes (GI.1a and GI.1c) have been detected in China to date. In 2010, a new RHDV variant with a unique genetic and antigenic profile was identified in France, designated RHDV2, which rapidly spread throughout continental Europe and nearby islands. Here, we report the first outbreak of RHD induced by RHDV2 (GI.2) in rabbit farms in the Sichuan province of China. We conducted haemagglutination tests and phylogenetic analysis of the new RHDV isolate SC2020/04, which was identified as a non‐haemagglutinating strain belonging to the RHDV2 (GI.2) genogroup. Considering the serious risk of RHDV2 to the Chinese rabbit industry, the circulation of RHDV2 in the population should be carefully monitored in China.

RHDV2 epidemic in UK pet rabbits. Part 2: PCR results and correlation with vaccination status

Objective

To report PCR results and vaccination status of rabbits with rabbit haemorrhagic disease following an investigation into sudden or unexpected death.

Materials and Methods

PCR testing for RHDV2 and RHDV1 was performed on rabbit liver samples at two laboratories. Laboratory A reported results as positive or negative; Laboratory B reported results quantitatively as RNA copies per mg liver, categorised as negative, inconclusive or positive. The vaccination status of rabbits with both histopathological features of rabbit haemorrhagic disease and positive PCR test results were collated.

Results

PCR results matched histopathological findings in 188 of 195 (96%) cases. Seven individuals showed equivocal results, all of which had histopathological features of RHD but three tested PCR‐negative and four results conflicted between laboratories. RHDV2 was the serotype detected in all PCR‐positive cases. Histological features of rabbit haemorrhagic disease and PCR test results were positive in 125 rabbits; 51 unvaccinated, 56 in‐date with Nobivac Myxo‐RHD and 13 vaccinated against RHDV2 – although nine of these were vaccinated within 10 days of death.

Clinical Significance

PCR testing complements histopathology in cases of sudden death in rabbits by confirming the diagnosis and identifying virus serotype, but there can be false negatives. Although RHDV2 is currently prevalent in UK pet rabbits, vaccination against both RHDV1 and RHDV2 is recommended. Failures of RHDV2 vaccine are infrequent.

Widespread occurrence of the non-pathogenic hare calicivirus (HaCV Lagovirus GII.2) in captive-reared and free-living wild hares in Europe

The Lagovirus genus comprises both pathogenic viruses as European brown hare syndrome virus (EBHSV- GII.1) and rabbit hemorrhagic disease viruses (RHDV-GI.1 and RHDV2-GI.2), that principally infect European brown hares (Lepus europeaus) and European rabbits (Oryctolagus cuniculus), respectively, causing severe necrotic hepatitis, spleen enlargement and disseminated haemorrhage. This genus includes also non-pathogenic agents, such as rabbit calicivirus (RCV-E1 - GI.3) and the non-pathogenic hare Lagovirus, provisionally named hare calicivirus (HaCV - GII.2). The latter had been identified for the first time in 2012 in the gut contents and faeces of healthy young hares raised in a breeding farm. In this study, we further investigated the presence of HaCV by testing the intestinal tract of 621 wild hares collected between 2010 and 2018 in Northern and Central Italy, and in 2011 in Austria, Germany and Spain. These wild hares were found dead for causes other than EBHS or were healthy hares shot during the hunting season. Forty-three out of 322 hare samples from Italy and 14 out of 299 samples from Austria and Germany were positive for HaCV-GII.2 by RT-PCR using universal primers for lagoviruses and primers specific for HaCV. Sequence analysis of the full capsid protein gene conducted on 12 strains representative of different years and locations indicated that these viruses belong to the same, single cluster as the prototype strain initially identified at the hares' farm (HaCV_Bs12_1). The relatively high level of genetic variation (88% nt identity) within this cluster suggests HaCVs may have been circulating widely in Europe for some time.

Genotyping of rabbit hemorrhagic disease virus detected in diseased rabbits in Egyptian Provinces by VP60 sequencing

Background and Aim

Rabbit hemorrhagic disease (RHD) is an economically important disorder of rabbits, where infection results in severe losses to the meat and fur industries. Our goal was to characterize the RHD virus (RHDV) strains currently circulating in different regions of Egypt.

Materials and Methods

Fifty rabbits suspected of harboring RHDV from 15 Egyptian governorates were evaluated. Diseased rabbits were identified by clinical signs and postmortem lesions. RHDV was confirmed through hemagglutination assay (HA) and polymerase chain reaction (PCR). Partial sequencing of the VP60 gene was performed for genotyping.

Results

From 50 rabbits, we identified 16 cases of RHDV (32%) by HA and PCR, including seven males and nine females. We identified two distinct genotypes through sequencing of an amplified fragment of the virus VP60 gene. One group is composed of those circulating primarily in upper Egypt, which is closely related to the classical G3-G5 virus strains, and the second group, circulating predominantly in lower Egypt, was more closely related to the RHDV2 variant. The overall nucleotide sequence identity ranged from 78.4% to 100%, and identity with the vaccine strains ranged from 78.8% to 91.1%.

Conclusion

Our results constitute important documentation of RHDV strains currently circulating in Egypt. The findings suggest that there may be a limit to the effectiveness of currently applied vaccine strains as this formulation may not cover all circulating strains. A wider investigation that includes both domestic and wild rabbits will be needed to identify appropriate control measures for this disease.

Construction and immunogenicity of novel bivalent virus-like particles bearing VP60 genes of classic RHDV(GI.1) and RHDV2(GI.2)

Rabbit hemorrhagic disease (RHD) is an acute, inflammatory, septic, and devastating infectious disease caused by Rabbit hemorrhagic disease virus (RHDV), which poses a serious threat to the rabbit industry. RHDV2 (GI.2/RHDVb), a recently reported new variant could cause RHD in wild populations, but also RHDV-vaccinated rabbits. For now, both RHDV and RHDV2 are the main causes of RHD. To develop a new subunit vaccine that could protect rabbits against both classic RHDV and RHDV2 infections, we constructed a recombinant baculovirus (Bac-classic RHDV VP60-RHDV2 VP60) containing the VP60 genes of classic RHDV and RHDV2. Both VP60 genes were well expressed simultaneously in Spodoptera frugiperda cells (Sf9) after infection with the recombinant baculovirus. Transmission electron microscopy showed that the recombinant VP60 self-assembled into virus-like particles (VLPs). The antigenicity and immunogenicity of the bivalent VLPs vaccine were examined with animal experiments. Our results demonstrated that both the humoral and cellular immune responses were efficiently induced in rabbits by a subunit vaccine based on the recombinant baculovirus. In addition, all rabbits immunized with the bivalent VLPs vaccine survived after challenged with classic RHDV, and showed no clinical signs of RHD, whereas all the rabbits in the negative control group died from classic RHDV infection and showed typical clinical signs of RHD. In summary, our results indicated that the recombinant baculovirus carrying two VP60 genes is a candidate construct from which to develop a bivalent VLPs vaccine against both classic RHDV and RHDV2 infections.

Bioinformatics analysis of capsid protein of different subtypes rabbit hemorrhagic disease virus

Background

Rabbit Hemorrhagic Disease Virus (RHDV) belongs to the Caliciviridae family, is a highly lethal pathogen to rabbits. Increasing numbers of studies have demonstrated the existence of antigenic variation in RHDV, leading to the emergence of a new RHDV isolate (RHDVb). However, the underlying factors determining the emergence of the new RHDV and its unpredictable epidemiology remain unclear. To investigate these issues, we selected more than 184 partial and/or complete genome sequences of RHDV from GenBank and analyzed their phylogenetic relationships, divergence, and predicted protein modification sites.

Results

Phylogenetic analysis showed that classic RHDV isolates, RHDVa, and RHDVb formed different clades. It’s interesting to note that RHDVa being more closely related to classic RHDV than RHDVb, while RHDVb had a closer genetic relationship to Rabbit Calicivirus (RCV) than to classic RHDV isolates. Moreover, divergence analysis suggested that the accumulation of amino acid (aa) changes might be a consequence of adaptive diversification of capsid protein (VP60) during the division between classical RHDV, RHDVa, RHDVb, and RCV. Notably, the prediction of N-glycosylation sites suggested that RHDVb subtypes had two unique N-glycosylation sites (aa 301, 362) but lacked three other N-glycosylation sites (aa 45, 308, 474) displayed in classic RHDV and RHDVa VP60 implying this divergence of N-glycosylation sites in RHDV might affect viral virulence. Analysis of phosphorylation sites also indicated that some phosphorylation sites in RHDVa and RHDVb differed from those in classic RHDV, potentially related to antigenic variation in RHDV.

Conclusion

The genetic relationship between RHDVb and RCV was closer than classic RHDV isolates. Moreover, compared to RHDV and RHDVa, RHDVb had two unique N-glycosylation sites but lacked three sites, which might affect the virulence of RHDV. These results may provide new clues for further investigations of the origin of new types of RHDV and the mechanisms of genetic variation in RHDV.

Monitoring of the novel rabbit haemorrhagic disease virus type 2 (GI.2) epidemic in European wild rabbits (Oryctolagus cuniculus) in southern Spain, 2013-2017

Rabbit hemorrhagic disease (RHD) is a highly infectious disease in European rabbits (Oryctolagus cuniculus), caused by a virus belonging to the genus Lagovirus (RHDV; family Caliciviridae). In 2010, a new genotype of RHDV (RHDV2 or RHDVb, currently designated GI.2) emerged in France, affecting both domestic rabbits, even those vaccinated for the classical RHDV genotypes (currently designated GI.1) and wild rabbits. GI.2 was subsequently identified in other European countries. The aim of the present study was to monitor the GI.2 epidemic in wild rabbits in Andalusia (southern Spain) during the period 2013-2017. At the beginning of summer 2013, high mortalities were detected in wild rabbit populations in southern Spain. A total of 96 affected hunting or protected areas were surveyed. The first outbreak was observed on June 2013. The number of outbreaks sharply increased in 2013 and 2014, with a decreasing trend being observed during the following years. The spatial distribution of GI.2 was not homogeneous, since most of the detected outbreaks were concentrated in the western part of Andalusia. The outbreaks peaked in winter and spring and have been detected in the last five consecutive years, which suggests endemic circulation of GI.2 in wild rabbit populations in Spain. A total of 190 dead rabbits from 87 of the 96 areas surveyed were collected during the study period. Mortality affected rabbits of different age classes, including kittens. RT-PCR confirmed the presence of GI.2 RNA in the livers of 185 of the 190 (97.4%) rabbits. Phylogenetic analysis performed on eleven samples collected in different provinces of Andalusia between 2013 and 2017, showed high nucleotide identity with GI.2 strains Spain, France and Portugal. The results constitute an important step in understanding of the emergence and spread of GI.2 in this country and will provide valuable information for the development of surveillance programs in Europe.

Immunogenicity in Rabbits of Virus-Like Particles from a Contemporary Rabbit Haemorrhagic Disease Virus Type 2 (GI.2/RHDV2/b) Isolated in The Netherlands

Rabbit haemorrhagic disease virus (RHDV) type 2 (GI.2/RHDV2/b) is an emerging pathogen in wild rabbits and in domestic rabbits vaccinated against RHDV (GI.1). Here we report the genome sequence of a contemporary RHDV2 isolate from the Netherlands and investigate the immunogenicity of virus-like particles (VLPs) produced in insect cells. RHDV2 RNA was isolated from the liver of a naturally infected wild rabbit and the complete viral genome sequence was assembled from sequenced RT-PCR products. Phylogenetic analysis based on the VP60 capsid gene demonstrated that the RHDV2 NL2016 isolate clustered with other contemporary RHDV2 strains. The VP60 gene was cloned in a baculovirus expression vector to produce VLPs in Sf9 insect cells. Density-gradient purified RHDV2 VLPs were visualized by transmission electron microscopy as spherical particles of around 30 nm in diameter with a morphology resembling authentic RHDV. Immunization of rabbits with RHDV2 VLPs resulted in high production of serum antibodies against VP60, and the production of cytokines (IFN-γ and IL-4) was significantly elevated in the immunized rabbits compared to the control group. The results demonstrate that the recombinant RHDV2 VLPs are highly immunogenic and may find applications in serological detection assays and might be further developed as a vaccine candidate to protect domestic rabbits against RHDV2 infection.

Genetic characterization and phylogenetic analysis of rabbit hemorrhagic disease virus isolated in Tunisia from 2015 to 2018

Two distinct genotypes responsible for rabbit hemorrhagic disease (RHD) are reported, GI.1 (RHDV) and GI.2 (RHDV2). Vaccines based on these two genotypes are only partially cross-protective. Hence, knowing which genotype is circulating is important for appropriate control measures. We have investigated 25 field samples isolated between 2015 and 2018 from rabbits with clinical signs of RHD. Only GI.2 (RHDV2) is currently circulating in Tunisia. All Tunisian samples were grouped together with typical genotypic and phenotypic mutations. Therefore, we recommend initiating an extensive preventive vaccination program based on GI.2 vaccines in addition to a regular monitoring of the circulating lagoviruses.

Prevalence, Morphological and Molecular Phylogenetic Analyses of the Rabbit Pinworm, Passalurus ambiguus Rudolphi 1819, in the Domestic Rabbits Oryctolagus cuniculus

INTRODUCTION

Passalurus ambiguus, a pinworm nematode parasite, infects domestic and wild rabbits, hares, and rodents worldwide.

MATERIALS AND METHODS

The current parasitological study was performed during January-December 2016, to investigate helminth parasites infecting the domestic rabbit species Oryctolagus cuniculus at the Department of Animal Production, Faculty of Agriculture, Cairo University, Cairo, Egypt.

RESULTS

Of the twenty rabbit specimens examined for gastrointestinal nematodes, 75% were infected with adult oxyurid species, which were morphologically characterized using light and scanning electron microscopy studies. The oxyurid species had a triangular mouth opening surrounded by simple lips with four cephalic papillae and a pair of lateral amphidial pores with three teeth-like structures, an esophagus divided into a cylindrical corpus and globular bulb supported internally with tri-radiate valvular apparatus, and four caudal papillae distributed on the posterior end of males with a single short protruding spicule and ovijector apparatus opening ventrally by the vulva, surrounded by protruded lips in female worms. The species were compared morphometrically with other Passalurus species described previously; light differences were found in different body part sizes. Molecular characterization based on 18 small subunit (SSU) rDNA sequences showed ~ 85% similarity with other Chromadorea species. A preliminary genetic comparison between the 18S rDNA sequences of the isolated parasite and those of other oxyurid species suggested that it belonged to Passalurus ambiguus. The 18S rDNA sequence of the parasite was deposited in GenBank (accession no., MG310151.1).

CONCLUSION

The 18S rDNA gene of P. ambiguus was shown to yield a unique genetic sequence that confirms its taxonomic position within the Oxyuridae family.

Molecular methods in detection and epidemiologic studies of rabbit and hare viruses: a review

Various PCR-based assays for rabbit viruses have gradually replaced traditional virologic assays, such as virus isolation, because they offer high-throughput analysis, better test sensitivity and specificity, and allow vaccine and wild-type virus strains to be fully typed and differentiated. In addition, PCR is irreplaceable in the detection of uncultivable or fastidious rabbit pathogens or those occurring in low quantity in a tested sample. We provide herein an overview of the current state of the art in the molecular detection of lagomorph viral pathogens along with details of their targeted gene or nucleic acid sequence and recommendations for their application. Apart from the nucleic acids-based methods used for identification and comprehensive typing of rabbit viruses, novel methods such as microarray, next-generation sequencing, and mass spectrometry (MALDI-TOF MS) could also be employed given that they offer greater throughput in sample screening for viral pathogens. Molecular methods should be provided with an appropriate set of controls, including an internal amplification control, to confirm the validity of the results obtained.

Overcoming species barriers: an outbreak of Lagovirus europaeus GI.2/RHDV2 in an isolated population of mountain hares (Lepus timidus)

Background

Prior to 2010, the lagoviruses that cause rabbit hemorrhagic disease (RHD) in European rabbits (Oryctolagus cuniculus) and European brown hare syndrome (EBHS) in hares (Lepus spp.) were generally genus-specific. However, in 2010, rabbit hemorrhagic disease virus 2 (RHDV2), also known as Lagovirus europaeus GI.2, emerged and had the distinguishing ability to cause disease in both rabbits and certain hare species. The mountain hare (Lepus timidus) is native to Sweden and is susceptible to European brown hare syndrome virus (EBHSV), also called Lagovirus europaeus GII.1. While most mountain hare populations are found on the mainland, isolated populations also exist on islands. Here we investigate a mortality event in mountain hares on the small island of Hallands Väderö where other leporid species, including rabbits, are absent.

Results

Post-mortem and microscopic examination of three mountain hare carcasses collected from early November 2016 to mid-March 2017 revealed acute hepatic necrosis consistent with pathogenic lagovirus infection. Using immunohistochemistry, lagoviral capsid antigen was visualized within lesions, both in hepatocytes and macrophages. Genotyping and immunotyping of the virus independently confirmed infection with L. europaeus GI.2, not GII.1. Phylogenetic analyses of the vp60 gene grouped mountain hare strains together with a rabbit strain from an outbreak of GI.2 in July 2016, collected approximately 50 km away on the mainland.

Conclusions

This is the first documented infection of GI.2 in mountain hares and further expands the host range of GI.2. Lesions and tissue distribution mimic those of GII.1 in mountain hares. The virus was most likely initially introduced from a concurrent, large-scale GI.2 outbreak in rabbits on the adjacent mainland, providing another example of how readily this virus can spread. The mortality event in mountain hares lasted for at least 4.5 months in the absence of rabbits, which would have required virus circulation among mountain hares, environmental persistence and/or multiple introductions. This marks the fourth Lepus species that can succumb to GI.2 infection, suggesting that susceptibility to GI.2 may be common in Lepus species. Measures to minimize the spread of GI.2 to vulnerable Lepus populations therefore are prudent.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1694-7) contains supplementary material, which is available to authorized users.

Robust Innate Immunity of Young Rabbits Mediates Resistance to Rabbit Hemorrhagic Disease Caused by Lagovirus Europaeus GI.1 But Not GI.2

The rabbit caliciviruses Lagovirus europaeus GI.1 and GI.2 both cause acute necrotizing hepatitis in European rabbits (Oryctolagus cuniculus). Whilst GI.2 is highly virulent in both young and adult rabbits, rabbits younger than eight weeks of age are highly resistant to disease caused by GI.1, although they are still permissive to infection and viral replication. To investigate the underlying mechanism(s) of this age related resistance to GI.1, we compared liver transcriptomes of young rabbits infected with GI.1 to those of adult rabbits infected with GI.1 and young rabbits infected with GI.2. Our data suggest that kittens have constitutively heightened innate immune responses compared to adult rabbits, particularly associated with increased expression of major histocompatibility class II molecules and activity of natural killer cells, macrophages, and cholangiocytes. This enables them to respond more rapidly to GI.1 infection than adult rabbits and thus limit virus-induced pathology. In contrast, these responses were not fully developed during GI.2 infection. We speculate that the observed downregulation of multiple genes associated with innate immunity in kittens during GI.2 infection may be due to virally-mediated immunomodulation, permitting fatal disease to develop. Our study provides insight into the fundamental host⁻pathogen interactions responsible for the differences in age-related susceptibility, which likely plays a critical role in defining the success of GI.2 in outcompeting GI.1 in the field.

An Outbreak of Rabbit Hemorrhagic Disease in Finland

Rabbit hemorrhagic disease (RHD) was detected in European rabbits ( Oryctolagus cuniculus) for the first time ever in Finland in 2016. Reports of dead feral rabbits in Helsinki started to accumulate from April 2016. The Finnish Food Safety Authority Evira received the first animals in late April, and the main necropsy finding was severe, acute necrotizing hepatitis. Genetic material from RHD virus (RHDV) was detected in the liver and was further characterized as RHDV2. The Finnish virus did not group with RHDV strains from a concurrent outbreak in neighboring Sweden, suggesting another origin. The outbreak peaked in May and lasted until August, after which sightings of both live and dead rabbits became rare. No major outbreaks in domestic rabbits were observed, although infection in one pet rabbit was confirmed.

Elucidation of the pathology and tissue distribution of Lagovirus europaeus GI.2/RHDV2 (rabbit haemorrhagic disease virus 2) in young and adult rabbits (Oryctolagus cuniculus)

Lagovirus europaeus GI.2, also known as RHDV2 or RHDVb, is an emerging virus that causes rabbit haemorrhagic disease (RHD) in European rabbits (Oryctolagus cuniculus). In contrast to L. europaeus GI.1 (or RHDV/RHDVa) viruses that are only pathogenic for adults, GI.2 causes clinical disease in both adults and kittens. However, detailed descriptions of the pathology of this virus that may provide insight into its pathogenicity and emergence are lacking. Using an Australian GI.2 field strain isolated in 2015, we provide the first detailed description of pathology, viral antigen distribution and tissue load of GI.2 in adult and 5-week old New Zealand white rabbits using histology, immunohistochemistry and RT-qPCR. Liver was the target organ, but in contrast to GI.1 viruses, lesions and inflammatory responses did not differ between adults and kittens. Lymphocytic inflammation, proposed to be protective in kittens infected with GI.1, was notably absent. We also present the first descriptions of bone marrow changes in RHD, including decreased myeloid-to-erythroid ratio. Consistent with other pathogenic lagoviruses, intracellular viral antigen was demonstrated in hepatocytes and cells of the mononuclear phagocytic system. In terminal stages of disease, viral loads were highest in liver, serum and spleen. Despite the small sample size, our data suggest that unlike early European GI.2 strains, the pathogenicity of the Australian GI.2 virus is similar to GI.1 viruses. Additionally, GI.2 was fatal for all (n = 5) inoculated kittens in this study. This may significantly alter RHD epidemiology in the field, and may impact biocontrol programs for invasive rabbits in Australia where GI.1 viruses are intentionally released.

Substantial numerical decline in South Australian rabbit populations following the detection of rabbit haemorrhagic disease virus 2

Lagovirus europaeus GI.2, also commonly known as rabbit haemorrhagic disease virus 2, was first detected at two long-term monitoring sites for European rabbits, Oryctolagus cuniculus, in South Australia, in mid-2016. Numbers of rabbits in the following 12-18 months were reduced to approximately 20 per cent of average numbers in the preceding 10 years. The impact recorded at the two South Australian sites, if widespread in Australia and persistent for several years, is likely to be of enormous economic and environmental benefit.

Host-Specific Glycans Are Correlated with Susceptibility to Infection by Lagoviruses, but Not with Their Virulence

Rabbit hemorrhagic disease virus (RHDV) and European brown hare syndrome virus (EBHSV) are two lagoviruses from the family Caliciviridae that cause fatal diseases in two leporid genera, Oryctolagus and Lepus, respectively. In the last few years, several examples of host jumps of lagoviruses among leporids were recorded. In addition, a new pathogenic genotype of RHDV emerged, and many nonpathogenic strains of lagoviruses have been described. The molecular mechanisms behind host shifts and the emergence of virulence are unknown. Since RHDV uses glycans of the histo-blood group antigen type as attachment factors to initiate infection, we studied if glycan specificities of the new pathogenic RHDV genotype, nonpathogenic lagoviruses, and EBHSV potentially play a role in determining the host range and virulence of lagoviruses. We observed binding to A, B, or H antigens of the histo-blood group family for all strains known to primarily infect European rabbits (Oryctolagus cuniculus), which have recently been classified as GI strains. However, we could not explain the emergence of virulence, since similar glycan specificities were found in several pathogenic and nonpathogenic strains. In contrast, EBHSV, recently classified as GII.1, bound to terminal β-linked N-acetylglucosamine residues of O-glycans. Expression of these attachment factors in the upper respiratory and digestive tracts in three lagomorph species (Oryctolagus cuniculus, Lepus europaeus, and Sylvilagus floridanus) showed species-specific patterns regarding susceptibility to infection by these viruses, indicating that species-specific glycan expression is likely a major contributor to lagovirus host specificity and range.IMPORTANCE Lagoviruses constitute a genus of the family Caliciviridae comprising highly pathogenic viruses, RHDV and EBHSV, that infect rabbits and hares, respectively. Recently, nonpathogenic strains were discovered and new pathogenic strains have emerged. In addition, host jumps between lagomorphs have been observed. The mechanisms responsible for the emergence of pathogenicity and host species range are unknown. Previous studies showed that RHDV strains attach to glycans expressed in the upper respiratory and digestive tracts of rabbits, the likely portals of virus entry. Here, we studied the glycan-binding properties of novel pathogenic and nonpathogenic strains looking for a link between glycan binding and virulence or between glycan specificity and host range. We found that glycan binding did not correlate with virulence. However, expression of glycan motifs in the upper respiratory and digestive tracts of lagomorphs revealed species-specific patterns associated with the host ranges of the virus strains, suggesting that glycan diversity contributes to lagovirus host ranges.

Large-scale lagovirus disease outbreaks in European brown hares (Lepus europaeus) in France caused by RHDV2 strains spatially shared with rabbits (Oryctolagus cuniculus)

Rabbit haemorrhagic disease virus (RHDV) is a lagovirus that causes rabbit haemorrhagic disease (RHD) in European rabbits (Oryctolagus cuniculus). In 2010, a new genotype called RHDV2 emerged in France. It exhibits a larger host range than classical RHDV strains by sporadically infecting different hare species, including the European hare (Lepus europaeus). Phylogenetic analyses revealed that closely related RHDV2 strains circulate locally in both hares and rabbits, and therefore that RHDV2 strains infecting hares do not belong to a lineage that has evolved only in this species. We showed that RHDV2 is widely distributed in France and that it was responsible for more than a third of cases of lagovirus disease in European hare populations in 2015. The oldest RHDV2 positive hare was sampled in November 2013 and we reported two hares co-infected by EBHSV and RHDV2. All together, our results raise important epidemiological and evolutionary issues. In particular, along with the potential emergence of recombinant EBHSV/RHDV2 strains in hares, the enlargement of the host range changes the host population structure of RHDV2 and may alter the impact of the virus on rabbit and hare populations.